It has previously been proposed to construct an electrochemical sensor by applying an electrode layer on a solid electrolyte body by sintering. This electrode layer is applied at least at the side of the solid electrolyte body exposed to the gas to be tested. To provide protection to the electrode, the electrode layer is formed of a mixture of a noble metal powder and a ceramic powder. The ceramic powder typically is of similar composition as that of the solid electrolyte body (see German published patent application DE-AS No. 26 31 721). Such sensors require a considerable amount of noble metal, typically platinum, and in the sensors as proposed, the platinum content may be between 30-50% (by volume) in order to provide sufficient electrical conductivity to the electrodes-ceramic composite layer, so that a suitable output voltage can be derived from the sensor.
The price of noble metals continues to rise and, in mass production items, it is desirable to reduce the noble metal content as much as possible so that the costs of such high-volume articles can be kept reasonable and reduced. A sensor which has an electrode layer with a high content of noble metal, further, is not as resistant to the corrosive influences of hot combustion gases as desirable. Platinum is comparatively soft and is gradually eroded, which causes difficulties in the cohesion of the overall electrode layer.